San Francisco, California - Researchers have discovered that a coronavirus epidemic broke out in the East Asia region more than 20,000 years ago.

Traces of the outbreak are evident in the genetic make-up of people from that area, experts say.

In the past 20 years, there have been three major outbreaks of coronavirus epidemics.

These have been SARS-CoV leading to Severe Acute Respiratory Syndrome (SARS), which originated in China in 2002 and killed more than 800 people. MERS-CoV led to Middle East Respiratory Syndrome (MERS), which killed more than 850 people, while SARS-CoV-2, which causes Covid-19, has killed more than 3.8 million people.

But the new study of the evolution of the human genome has revealed another large coronavirus epidemic broke out thousands of years earlier.

Professor Kirill Alexandrov, from CSIRO-QUT Synthetic Biology Alliance and Queensland University of Technology's Centre for Genomics and Personalised Health, is part of a team of researchers from the University of Arizona, the University of California San Francisco, and the University of Adelaide.

He said: "The modern human genome contains evolutionary information tracing back tens of thousands of years, like studying the rings of a tree gives us insight into the conditions it experienced as it grew."

Researchers used data from the 1000 Genomes Project, which is the largest public catalog of common human genetic variation, and looked at the changes in the human genes coding for SARS-CoV-2 interacting proteins.

They then synthesized both human and SARS-CoV-2 proteins, without using living cells, and showed that these interacted directly, and specifically pointed to the conserved nature of the mechanism coronaviruses use to invade cells.

Alexandrov said: "Computational scientists on the team applied evolutionary analysis to the human genomic dataset to discover evidence that the ancestors of East Asian people experienced an epidemic of a coronavirus-induced disease similar to Covid-19."

East Asian people come from the area that is now China, Japan, Mongolia, North Korea, South Korea and Taiwan.

"In the course of the epidemic, selection favored variants of pathogenesis-related human genes with adaptive changes presumably leading to a less severe disease," Alexandrov said.

He added: "By developing greater insights into the ancient viral foes, we gain understanding of how genomes of different human populations adapted to the viruses that have been recently recognized as a significant driver of human evolution.

"Another important offshoot of this research is the ability to identify viruses that have caused epidemic in the distant past and may do so in the future.

"This, in principle, enables us to compile a list of potentially dangerous viruses and then develop diagnostics, vaccines and drugs for the event of their return."

The study is published in the journal Current Biology.